1. Field of the Invention
The present invention relates to an apparatus for the linearization of a digitally controlled oscillator (DCO), and more particularly, to an apparatus for the linearization of a DCO enabling the achievement of linearity within the entirety of the DCO by correcting an input directly applied to the DCO with the addition of a negative feedback loop, including a frequency table and a frequency-to-digital code mapper, to an input port of the DCO.
2. Description of the Related Art
Currently, mobile communication terminals need to support multiple modes and multiple bands, and the development period of products has also become shorter, and thus there is a need for a change in a traditional design methodology for a radio frequency (RF) front-end. As the minimum linewidth of a complementary metal-oxide semiconductor (CMOS) process is reduced, the implementation of RF blocks is undergoing a process of change from an existing analog method to a digital method in order that RF signals can be processed in the form of digital or discrete signals.
FIG. 1 is a block diagram illustrating a general digitally controlled oscillator (DCO).
Referring to FIG. 1, a DCO 100 includes a digital-to-analog converter (DAC) 101 and an analog voltage controlled oscillator (VCO) 102.
The DAC 101 converts a digital input value of an oscillator control word into an analog voltage form and outputs the converted voltage to the analog VCO 102. The analog VCO 102 receives the output voltage of the DAC 101 and outputs a continuous signal having an oscillation frequency corresponding to that voltage.
A DCO, which is a core block of a digital frequency synthesizer, receives an input of an oscillator control word and outputs a continuous signal having an output frequency corresponding to that oscillator control word. However, due to external environments such as process variation, voltage, and temperature, it is impossible to output an exact frequency corresponding to the oscillator control word without a tuning process.
A code gain of the DCO is defined as a variation in the output frequency of the DCO with respect to a variation in a Least Significant Bit (LSB) of the oscillator control word. In general, the code gain of the DCO is not consistent in an entirety of an oscillator control word area. When the code gain is not consistent, the characteristics of the digital frequency synthesizer may be variable according to each oscillator control word, so variations in performance may be undesirably large.
Also, when the digital frequency synthesizer is generally designed, other blocks are designed with an assumption that the code gain is consistent, so it may be desirable to make the code gain consistent. Particularly, when a transmitter is designed by using a direct modulation method, the code gain of the DCO is required to be consistent. This is because when the code gain is not consistent, distortion of transmitted data may occur.